Barack Obama's campaign yesterday rushed to proclaim his support for "clean coal" technology after remarks by running mate Joe Biden cast doubts on Democratic friendliness to the coal industry.

In a videotaped exchange with an environmental campaigner in Ohio, Biden allowed Republicans to change the subject from the financial gloom that has put John McCain on the defensive this week.

Asked why he and Obama backed the expensive prospect of capturing and storing carbon dioxide emitted from coal-fired power plants, Biden told the campaigner: "We're not supporting clean coal … No coal plants here in America."

Biden's comments contradict Obama's public promotion of "clean coal" as well as a more controversial scheme to turn coal into liquid fuel.

Environmentalists have chided Obama for supporting those ideas, but Biden's spontaneous remark could do the Democrats greater damage with voters in coal-producing states such as Ohio and Virginia.

"Senator Obama truly is a friend of the coal industry," Rick Boucher, a Democratic congressman from Virginia's coal country, told reporters. "His record … and his position in terms of the coal industry's future give us confidence."

McCain did not challenge Obama's support for carbon capture and sequestration (CCS) at power plants, which is years from coming to fruition in the US.

But his fellow Republicans unveiled a Coalition to Protect Coal Jobs to accuse Biden of pandering to voters by criticising coal in Ohio while proudly telling Virginians he comes from a line of coal miners.

"[Democrats] are saying one thing in front of a large group, and when they actually are asked their true feelings, that's when we really hear the attacks on coal," Shelley Moore Capito, a Republican congresswoman from West Virginia, told reporters.

The Obama camp responded by condemning McCain for his resistance to renewable energy tax incentives that are slated for approval in Congress this week.

The US solar and wind industries rely on tax credits to continue growing, but those benefits were defeated by one vote last year after McCain withheld his backing.

Though the Republican touts his support for solar and wind power on the campaign trail, McCain voted to block the tax credits because they were paid for by the repeal of tax benefits for oil companies.

McCain has not spoken about this week's renewable-energy plan – which includes more than $1.5bn in new tax credits for CCS – but is considered a likely opponent, given that it also reverses some oil industry incentives.

Jeff Bingaman, chairman of the Senate energy committee, said the solar and wind credits likely would pass without McCain's vote but added that his "voiced opposition to it is obviously a concern".

Of serious concern to some US environmental campaigners is a plank in the clean-energy tax plan that reverses a 30-year-old ban on using government-owned land for private oil shale extraction.

Conservatives have long proposed taking oil shale from the ground in western US states to produce more domestic fuel. Like "clean coal" and coal-to-liquid fuel production, oil shale is still in its infancy and poses significant environmental threats.

"It requires technology we don't currently have," Craig Thompson, a college professor and former president of the Wyoming Wildlife Federation, said.

"It produces a fossil fuel that, at best, may delay by a few years a transition to sustainable energy resources that we're going to have to make anyway in the future."

Obama is generally supportive of the clean-energy tax credits, which were expected to clear the US Senate late yesterday.